Reversing "Oxidation" on Stamps
A gentle bath in a two to three percent hydrogen peroxide solution will restore the colour in stamps that have
lead based inks that have darkened due to exposure to trace amounts of acid. If the colour does not change
after a half an hour or so, "oxidation" is not the culprit. This treatment works for restoring colour to the 3c
small Queens of Canada. By a different chemical mechanism it will also restore the colour of the "muddy
waters" variety of the Canadian 1898 Map Stamp. Research the stamp pigment before using hydrogen
peroxide, as vegetable based dyes used in later years may be irreversibly bleached by this treatment.
http://stamps.org/cac/resources/art.../artg003.pdf